(1) Field of the Invention
The invention relates to compressors, and more particularly to screw-type compressors.
(2) Description of the Related Art
Screw-type compressors are commonly used in air conditioning and refrigeration applications. In such a compressor, intermeshed male and female lobed rotors or screws are rotated about their axes to pump the working fluid (refrigerant) from a low pressure inlet end to a high pressure outlet end. During rotation, sequential lobes of the male rotor serve as pistons driving refrigerant downstream and compressing it within the space (compression pocket) between an adjacent pair of female rotor lobes and the housing. Likewise sequential lobes of the female rotor produce compression of refrigerant within a male rotor compression pocket between an adjacent pair of male rotor lobes and the housing. In one implementation, the male rotor is coaxial with an electric driving motor and is supported by bearings on inlet and outlet sides of its lobed working portion. There may be multiple female rotors engaged to a given male rotor or vice versa. With such a compressor, male and female compression pockets may also have multiple inlet and outlet ports.
When a compression pocket is exposed to an inlet port, the refrigerant enters the pocket essentially at suction pressure. As the pocket continues to rotate, at some point during its rotation, the pocket is no longer in communication with the inlet port and the flow of refrigerant to the pocket is cut off. Typically the inlet port geometry is arranged in such a way that the flow of refrigerant is cut off at the time in the cycle when the pocket volume reaches its maximum value. Typically the inlet port geometry is such that both male and female compression pockets are cut off at the same time. The inlet port is typically a combination of an axial port and a radial port. After the inlet port is closed, the refrigerant is compressed as the pockets continue to rotate and their volume is reduced. At some point during the rotation, each compression pocket intersects the associated outlet port and the closed compression process terminates. Typically outlet port geometry is such that both male and female pockets are exposed to the outlet port at the same time. As with the inlet port, the outlet port is normally a combination of an axial port and a radial port. By combining axial and radial ports into one design configuration, the overall combined port area is increased, minimizing throttling losses associated with pressure drop through a finite port opening area. In an exemplary three-rotor configuration, the inlet and outlet ports are respectively formed at common inlet and outlet plenums.
The compressor may be designed and sized for its intended use (e.g., to provide a given compression or volume index and operate at a given flow at a given speed or combination thereof). Different compressors or at least different components (rotors, motors, and the like) may be required for different uses.